A desire to be able to distinguish targets from clutter has always has been an objective with radar sensors. Traditionally this has been based on the fact that the velocity of a moving target will be different from background disturbances such as present clutter. Clutter echoes may, for instance, result from small gradients in a surrounding medium like air or a surrounding water surface. Therefore different Doppler filters have been developed to solve this task.
Thus, all present solutions generally seem to be based on the Doppler signal information extracted from received echo signals. However typical solutions of today utilise coded long pulses, for instance using a binary phase code or spread spectrum signals operating at large receiver bandwidths. Some of these signals resemble signal noise or clutter signals or a jamming signal source.
Such broadband signal radar signals generally do not exhibit a pronounced carrier, which means that a regular velocity filtering can not take place using ordinary Doppler methods. However, with new broadband radar systems there will be further possibilities to measure other echo parameters and to construct filters which, for instance, may directly filter out reflections from objects having metallic surfaces and separate those for example from those targets with generally non-metallic surfaces.